Apparatus for making prestressed concrete bodies



May 28, 1968 J. A. SHAW E AL 3,384,942

APPARATUS FOR MAKING PRESTRESSED CONCRETE BODIES Filed Nov. 17, 1965 4 Tl L157 53 FlG.2 23 569%- INVENTORS JOHN A, SHAW DANIEL E-OLIVIERATTORNEY United States Patent 3,384,942 APPARATUS FOR h'lAKlNGPRESTRESSED QNCRETE EOEIES John A. Shaw, Mountain Lakes, and Daniel E.Olivier, Berlminister, NJ assignors to International Pipe and CeramicsCorporation, larsippany, N..l., a corporation of Delaware Filed Nov. 17,1965, 522'. No. 508,199 8 (Ilaims. (Cl. 25--118) This invention relatesto apparatus for making prestressed concrete bodies.

Methods commonly used for manufacturing prestressed concrete bodies suchas prestressed pip-3s, columns,

beams, slabs and the like involve placing concrete in a mold throughwhich wires have been strung. Traction is applied to the wires and theyare held strained until the concrete sets. The strain in the wires isgenerally maintained by anchoring devices which frictionally grip ontothe wires. Because of the character of the anchoring devices more wireis used than is necessary for a given length of concrete body. Theeconomic loss in the manufacture of a prestressed product containingmany wires can be considerable. Moreover, such devices which rely on africtional grip are not wholly dependable to avoid slipping andreduction of tension in a wire before the concrete has set. Theavailable anchoring devices are expensive, shortlived and requirefrequent replacement. It is a purpose of the present inven tion toimprove upon the shortcomings of prior practices and to effect economiesin the manufacture of prestressed concrete bodies.

Among the objects of the invention is to provide forms of a wire and ofanchors therefor whereby an individual wire can be stressed to aprede'ermined tension and its ends broken off inside of a concrete bodythrough which the wi e extends. The wire is rovided with heads at itsends. The anchors engage the heads to stress the wire. Deformed sectionsof the wire adjacent the heads and the anchor at either end of the wireare provided with cooperating faces extending crosswise of andsubstantially parallel to the wire. These faces provide a positivebearing by which torsional force may be transmiited from the anchors tothe wire to break end portions from the portion thereof encased inconcrete. The ends of the wire are broken off simply by rotating theanchors about the axis of the wire.

According to the present invention, prestressing wires are individuallystrained and supported in tension by anchors which are constructed andarranged to enable the use of wires no longer or only a little longerthan the length of a molded concrete body.

A feature of the invention resides in the construction of elements of ananchor and of a cooperating element of a wire to provide anon-slippable, positive engagement between the anchor and the wire toassure that the wire remains under the stress to which it is initiallysubiected when the mold is prepared and until the concrete has hardened.

Another feature of the invention is in the adjustability of at least oneof the anchors in the axial direction of an engaged wire whereby theanchor is positionable relative to the mold for applying a desireddegree of stress to the wire.

Other objects, features and advantages of the present invention andpreferred ways of employing it will be evident from the accompanyingdrawing and the following detailed description of illustrativeembodiments of the invention.

In the drawing:

FIG. 1 is a longitudinal sectional view to one side of the axis of apipe mold;

FIG. 2 is an elevational view of one of the anchors; FIG. 3 is asectional view on line 3-3 of FIG. 2; FIG. 4 is an end view of anotheranchor;

FIG. 5 shows one of the halves of the anchor of FIG. 4 as viewed on line55 of FIG. 4;

FIG. 6 is illustrative of an end portion of a wire;

FIG. 7 shows the wire end of FIG. 6 turned through ninety degrees on itsaxis;

FIG. 8 illustrates an encased prestressing wire from which an endportion has been removed; and

FIG. 9 is a vertical section through a horizontal mold for molding aslab or the like.

The invention is described herein as applied to a stationary mold formolding a prestressed concrete pipe on a vertical axis, but it will beapparent that the principle embodied may be utilized in moldingprocedures utilizing rotating molds of various types, as well as withmolds for molding prestressed products other than pipes.

FIG. 1 illustrates a longitudinal section of an upright pipe mold 10 toone side of the axis of the mold. The view shOWn is in a planecontaining the central longitudinal axis of the mold and a tensionedwire 11. It is illustrative of any one of several other longitudinalsections containing tensioned wires. As is well understood, the numberof wires which are employed varies for different sizes of pipes and forpipes designed for different uses.

The lower end of the mold is supported on a base assembly 12, includinga ring 13 and a central shelf 14 attached to the ring by welds. In thepresent instance, the ring 13 is formed to project upwardly to provide aform 15 for shaping the inside surface of a bell or socket at the lowerend of a pipe. A transverse mold wall 16 is immovably fixed to the ring13 by welding, and this wall supports an outer mold shell 17 which isremovable therefrom for stripping a pipe from the mold. A gasket 18 isprovided to seal between the wall 16 and the outer shell 17.

A collapsible inner mold shell 19 in the form of a sleeve is supportedon the base assembly, and a gasket 20 effects a seal between the lowerend of the shell and the ring 13. A mold ring 21 rests on the upper endof the inner mold shell 19 and is sealed with respect thereto by agasket 22. While the form 15 and the ring 21 are shaped to form theinner surfaces of sockets for a double bell pressure pipe, it is evidentthat a straight walled pipe may be molded in a similar mold having acylindrical sleeve like the inner mold shell 19 for forming the innercylindrical surface of the pipe.

The upper ends of the inner and outer mold shells are spaced apart at adesired distance by an end wall 23 of the mold which is in the form of aring. The ring is fixed to a circular wall 24 supported concentricallyupon the top of the ring 21. The circular wall 24 is provided withopenings 25 through which concrete material may be introduced into thecavity of the mold between the shells.

The lower and upper rings 16 and 23 are substantially perpendicular tothe wire 11 and provide the support required for applying andmaintaining tension in the several wires employed. In making a doublebell pipe the mold cavity is filled with a concrete mix up to the levelindicated at 26.

. Lengths of wire are initially cut to an appropriate length for use inmaking a given length of pipe and the ends of each length are upset toform a head 27 at each end. The head may be described as having the formof a generally circular button enlarged laterally from the diameter ofthe wire.

A deformed section 28 is formed adjacent each head by laterallycompressing the wire between dies to form opposite faces 29, 30, in amanner well known in the art.

Before a wire is upset to form a head 27 and a deformed section 28, awasher 31 is placed upon the wire and fixed tightly in place thereon byupsetting the wire toward the sides of the washer. In upsetting thewire, the metal of the wire is forced radially outwardly beyond thediameter of the hole in the washer. A head 31, formed in this manner,prevents the wire from pulling away from the washer in the finishedproduct. While a circular washer may be used, a square or polygonalwasher is preferred as it is more resistant to turning in concrete andthus augments the resistance to torque of a wire bonded to concrete.

One end of a wire 11 is secured in place by an anchor 32 supported bythe lower wall 16. The anchor 32 has a cylindrical shank portion 33rotatable in a cylindrical bore 34 in its supporting wall 16, and atapered nose 35 projecting into the mold cavity. A flange 36 bears uponthe outside of the wall and holds the anchor in an axially fixedposition when the wire is tensioned. Either a bolt head 37 or anhexagonal recess 38 may be engaged by a wrench for rotating the anchorto break the wire, as will be explained more fully hereinafter.

Each of the several anchors used at the lower end of a mold isconstituted of two like halves 39 and 40, FIGS. 4 and 5, each piecehaving a fiat face 41 in a plane containing the axis of the anchor.

The interior of the anchor 32 is formed to receive an end portion of awire 11. For this purpose the anchor is provided with a longitudinalrecess 42 opening toward the mold cavity at one end and extending into awidened circular chamber 43 at its other end. Shoulder 46 provides anabutment surface for engaging and bearing upon the laterally extendingunderside of a head on a wire.

As more clearly appearing in FIGS. 4 and 5, one half of the recess 42and of the chamber 43' is disposed in each half-piece 39 and 40. Theopposite walls 44 and 45 of the recess are spaced apart a distanceslightly greater than the minimum thickness of a deformed section 28(FIG. 7), but no greater than the broadest width thereof (FIG. 6) sothat the side walls 44 and 45 will engage the deformed section uponrotation of the anchor. Breakage of the wire occurs at or close to theend face of the nose 35 in the general vicinity indicated at 47, FIG. 6.The wider walls of the recess are preferably disposed perpendicularly tothe plane of division between, the two halves 39 and 40 of the anchor.

The wire 11 is tensioned between the anchor 32 and an anchor 48supported from the opposite end of the mold. Referring to FIGS. 1, 2 and3, the anchor 48 includees a round bar 49 and a member 50 which arecoupled together by the engagement of a threaded stem 51 at the lowerend of the bar with a threaded socket 52 in the member. A removable pin53 prevents rotation of the member 50 relative to the bar 49 when thebar is rotated. The bar and the member may be constituted in one piece,if desired.

The upper end of the bar 49 is provided with a bolt head 54 and a flange55 for engagement by the claws of a traction device (not shown). Thetraction device may consist of any conventional hydraulic jack havinglegs for hearing against the upper end of the mold. The bar 49 fitsslidably in a circular opening 56 in its supporting wall 23. An axialslot 57 in the bar 49 is engaged by a wedge 58 for holding the bar in aset position after the wire has been tensioned.

The member 50 is a solid one-piece member having a recess in the form ofT-slot 59 extending radially inwardly from the circumference of themember a distance sufficient to locate a headed wire on the central axisof the anchor. The recess provides a chamber for receiving a head 27 anda laterally extending surface pro viding an abutment shoulder againstwhich the underside of the head bears when the wire is stressed.

Shoulder 60 slopes downwardly toward the back of the recess. Theabutment surface thus provided assures that the wire will not movelaterally from the axis of the anchor when the anchor is rotated tobreak a wire. In lieu of a sloping surface, the central position of awire can be fixed by providing a countersink in a surface square to theaxis of an anchor for seating the head of a wire.

The axial stem 61 of the T-slot extends from the shoulder to the endface 62 a distance approximating the distance of a desired break-offpoint from the head of the wire. The broad side walls 63, 64 of theT-slot are spaced apart suificiently for the insertion of a deformedsection 28 edgewise into the slot. A hole 65 enables the entry of a toolto eject a broken-off end portion of a wire from the slot.

In assembling a wire in a mold, one end of the wire is attached to anupper anchor 48 which is then lowered to permit the lower end of thewire to be extended down- Wardly through the bore 34 in the lower moldwall 16. The two halves of a lower anchor 32 are placed about the headand the deformed section at the lower end of the wire. The lower anchor,thus assembled, is then inserted in the bore 34. A bolt 66 may be usedas a temporary support for the lower anchor.

The upper anchor 48 is then raised and attached to a traction devicewhich is operated to apply the force necessary to tension the wire tothe degree of unit stress desired. Tension in the wire is maintained bya wedge 58 when the traction device is disconnected from the upperanchor.

A mold containing the number of tensioned wires requisite for aparticular prestressed concrete body is filled with a suitable concretemix. Upon the hardening of the concrete the length of each wireextending between the anchors becomes bonded to the concrete.

The tensile stress in a wire becomes effective to prestress the concretein compression when the anchors are relieved of the pull of the wirethereon. This is accomplished simply by rotating the anchors to breakthe end portions of the wire contained therein from the length of wireembedded in the concrete. The loosened anchors may then be withdrawnaxially from their supports and the broken-off end portions removed fromwithin the anchors.

The wires and the procedure described may be used for castingprestressed concrete slabs. As demonstrated in FIG. 9, the ends of atensioned wire 67 are engaged by anchors 68 and 69, which arerespectively mounted on and supported by the respective end walls 70 and71 of a mold 72. The anchors 68 and 69 are respectively constructed likethe anchors 32 and 48. After the concrete 73 has set, the anchors arerotated to break off the end portions of the wire contained therein andso free the anchors and end walls from the restraining forcestheretofore brought to bear thereon by the anchored wire.

In practising the invention it is advantageous to apply a waterprooflubricant, such as a lithium soap grease, to all surfaces of the anchorswhich come into contact with concrete or the mold, and also to thesuperposed surfaces of the two halves of the split anchors. The coatingprevents leakage around the anchors and facilitates dismantling.

A hard drawn, spring steel wire having a tensile strength of the orderof 200,000 p.s.i. (140.6 kg./sq. mm.) and upwards is customarily used.in the construction of prestressed concrete pipes. For making pipes, thewires are prepared in lengths which provide for breaking the wire shortof the end face of a pipe. To effect this result, the wire lengthsshould be such that at least a portion of the length of each deformedsection is located inside of the mold cavity or inward from the innerface of an end wall of a mold.

A deformed section about /1 (19.1 mm.) long and having fiat faces spacedat about of the diameter of a wire is productive of satisfactoryresults. Upset heads having a diameter of about 1.75 times the diameterof the wire are adequate to resist the pull of the wires on the anchors.As explained hereinabove, the recesses in the anchors are soproportioned as to contain the heads and a sufiicient length of adeformed section to effect breakage close to the anchors.

While the form of apparatus herein shown and described is admirablyadapted to fulfill the objects primarily stated, it is to be understoodthat it is not intended to confine the invention to the forms hereindisclosed, for it is susceptible of embodiment in various forms allcoming within the scope of the claims which follow.

What is claimed is:

1. Apparatus for making a prestressed concrete body, comprising a mold,a wire strung across said mold, means for supporting said wire, saidsupporting means including an anchor at each end of said wire, said wirehaving at each of its ends an end portion including a head and adeformed section adjacent the head, said head projecting laterallybeyond the diameter of the wire, said deformed section having flat facesformed by compressing the wire radially, each of said anchors having arecess to receive one of said end portions of the wire, said recesshaving side walls extending axially inward from an end of the anchor anda wall extending laterally to said side walls, said laterally extendingwall providing an abutment shoulder, said abutment shoulder engaging thehead of the end portion to transmit force from said anchor to said wireto tension the Wire, said side walls of said recess spaced apart adistance greater than the minimum width of said deformed section but nogreater than its maximum width, said side walls engaging the flat faceson the end portion upon rotation of said anchor to transmit torque tothe end portion.

2. Apparatus according to claim 1, one of said anchors comprising twolike members separable at a plane passing through the axis of theanchor.

3. Apparatus according to claim 1, one of said anchors comprising asolid member in which said recess is in the form of a T-slot opening toa side of the member.

4. Apparatus according to claim 1, said wire having a washer fixedthereto in the vicinity of each of said anchors.

5. Apparatus for making a prestressed concrete body comprising a mold,anchoring means attached to each end of a wire extended across themolding cavity of the mold, a support for each of said anchoring means,each of said anchoring means havin a shank portion extending through anopening in the one of said supports on which it is supported and an endpart extending into the mold cavity, each anchoring means having arecess opentoward the mold cavity, said recess providing a shoulderdisposed laterally to said wire, said recess having side walls extendingfrom said shoulder to the mold cavity, a head at each end of said wire,said shoulder engaging one of said heads to prevent axial separation ofsaid anchoring means from said Wire when said wire is taut, a deformedsection of the wire adjacent each of said heads, each deformed sectionhaving faces extending generally crosswise of the wire, said side wallsof said recess spaced apart a distance greater than the minimum Width ofsaid deformed section but no greater than its maximum width, said sidewalls engaging said faces on the wire to transmit torque thereto uponrotation of the anchoring means.

6. Apparatus according to claim 5, said shank portion of one of saidanchoring means having means for attaching traction means theretowhereby to apply tension to said wire.

7. Apparatus according to claim 5, said end part of one of saidanchoring means coupled to said shank portion thereof.

8. Apparatus for making a prestressed concrete body, said apparatuscomprising a mold having Walls oppositely spaced from one another, afirst anchoring means supported on one of said walls, a second anchoringmeans supported on the other of said Walls, said first and said secondanchoring means each having a cylindrical shank portion extendingthrough an opening in its associated one of said walls, a wire extendedlengthwise between said first and said second anchoring means, a head ateach end of said wire, a deformed section on said wire adjacent each ofsaid heads, each deformed section having faces extending crosswise ofthe wire, said first and said second anchoring means each having alongitudinal recess opening at one end thereof toward the mold cavityand opening into a chamber at its other end, a shoulder extendinglaterally from said recess, said deformed section and said head at oneend of the wire respectively contained in said recess and said chamberin said first anchoring means, said deformed section and said head atthe other end of the wire respectively contained in said recess and saidchamber in said second anchoring means, the head at the respective endsof the wire bearing on said shoulder of said first and second anchoringmeans respectively, said first anchoring means comprising two likepieces having coextensive faces engaged at a plane containing thecentral axis of the anchoring means, each of said pieces providingone-half of the said recess and chamber of said first anchoring means,said second anchoring means comprising a bar and a member in which thesaid recess and chamber of the second anchoring means are disposed,means for coupling said member to said bar, whcrcby when a mid-portionof said wire is embedded in hardened concrete the wire may be brokenclose to said anchoring means by rotating said anchoring means.

References Cited UNITED STATES PATENTS 2,657,455 11/1953 I-lillberg25-131 X 2,905,491 9/1959 Olson. 3,234,619 2/1966 Vitz 251l8 3,332,1177/1967 McCarthy 287- X I. SPENCER OVERHOLSER, Primary Examiner.

J. R. BELL, Assistant Examiner.

1. APPARATUS FOR MAKING A PRESTRESSED CONCRETE BODY, COMPRISING A MOLD,A WIRE STRUNG ACROSS SAID MOLD, MEANS FOR SUPPORTING SAID WIRE, SAIDSUPPORTING MEANS INCLUDING AN ANCHOR AT EACH END OF SAID WIRE, SAID WIREHAVING AT EACH OF ITS ENDS AN END PORTION INCLUDING A HEAD AND ADEFORMED SECTION ADJACENT THE HEAD, SAID HEAD PROJECTING LATERALLYBEYOND THE DIAMETER OF THE WIRE, SAID DEFORMED SECTION HAVING FLAT FACESFORMED BY COMPRESSING THE WIRE RADIALLY, EACH OF SAID ANCHORS HAVING ARECESS TO RECEIVE ONE OF SAID END PORTIONS OF THE WIRE, SAID RECESSHAVING SIDE WALLS EXTENDING AXIALLY INWARD FROM AN END OF THE ANCHOR ANDA WALL EXTENDING LATERALLY TO SAID SIDE WALLS, SAID LATERALLY EXTENDINGWALL PROVIDING AN ABUTMENT SHOULDER, SAID ABUTMENT SHOULDER ENGAGING THEHEAD OF THE END PORTION TO TRANSMIT FORCE FROM SAID ANCHOR TO SAID WIRETO TENSION THE WIRE, SAID SIDE WALLS OF SAID RECESS SPACED APART ADISTANCE GREATER THAN THE MINIMUM WIDTH OF SAID DEFORMED SECTION BUT NOGREATER THAN ITS MAXIMUM WIDTH, SAID SIDE WALLS ENGAGING THE FLAT FACESON THE END PORTION UPON ROTATION OF SAID ANCHOR TO TRANSMIT TORQUE TOTHE END PORTION.